It has recently been discovered that a certain class of 2-haloacetanilide herbicides are particularly useful in safely controlling hard-to-kill perennial weeds, such as quackgrass, nutsedges and many others in the presence of a variety of crops including cotton, corn, and soybean. This new class of herbicides is described and claimed in Brazilian Pat. No. 887,997 issued Sept. 18, 1981. Two particularly effective herbicides within this class are N-(ethoxymethyl)-2'-trifluoromethyl-6'-methyl-2-chloroacetanilide and N-(ethoxymethyl)-2'-trifluoromethyl-6'-ethyl-2-chloroacetanilide.
The present invention relates to two intermediates in the production of compounds within this new class of herbicides. The present invention also relates to a process for preparing these two intermediates. This process generally involves nitration of a substituted benzotrifluoride compound.
Electrophilic substitution, such as nitration, halogenation, sulfonation, etc. of substituted benzene compounds is known in the art. It is also known that substituents on the benzene ring can affect both the reactivity and orientation of electrophilic substitution. Certain substituents can increase the reactivity of the benzene ring by donating electron density to the ring inductively or by resonance. Other groups withdraw electron density from the ring and thus reduce the reactivity of the ring.
Ring substituents can either direct electrophilic substitution at the ortho, para, or meta positions. With disubstituted benzene compounds, the two substituents can either reinforce or oppose each others directive influence. Activating substituents generally prevail over deactivating substituents. However, because of the sensitivity of electrophilic substitution to steric hindrance, there normally is little substitution between two substituents meta to each other regardless of the directive effect of the ring substituents. For example, nitration of meta-chloro-toluene results in only about 9% 2-nitro-3-chloro-toluene and about 59% 6-nitro-3-chloro-toluene. Nitration of 3-chloro benzoic acid results in only about 8% of the 2-nitro-3-chlorobenzoic acid.
It is known that a few specific meta-disubstituted benzene compounds direct a significant portion of electrophilic substitution between the two substituents. These specific compounds have an ortho-para directing substituent and a meta-directing substituent having an sp.sup.2 carbon atom bonded to the ring. Tomisek discloses that nitration of meta-toluic acid results in about 48% yield of the 2-nitro-3-toluic acid. (JACS 1588 (1946)) Hodgson discloses that nitration of 3-methoxybenzaldehyde results in about 56% yield of 2-nitro-3-methoxybenzaldehyde. (Aromatic Substitution Nitration and Halogenation by DeLa Mare & Ridd (1959)) However, Hodgson also discloses that nitration of the 3-hydroxybenzaldehyde which has an ortho-para directing substituent and a meta-directing substituent with an sp.sup.2 carbon atom bonded to the ring results in only about 3.5% yield of the 2-nitro-3-hydroxybenzaldehyde. Elliott predicts the orientation of aromatic substitution in a number of substituted benzene compound from M.O. calculations and predicts the nitration of 3-methyl benzotrifluoride in the 2 and 6 positions. Theochem 3 (4) 301 (1982). However, Elliott does not predict the 2 isomer as the major isomer.
It is an object of the present invention to provide new intermediate compounds useful in the production of compounds within a new class of 2-haloacetanilide herbicides.
It is another object of this invention to provide a process for producing these new intermediate compounds.
It is another object of this invention to provide a new aromatic nitration directing system.
Other objects and advantages will become apparent from the following disclosure.